On September 9, 2002, as the George W. Bush administration was launching its campaign to invade Iraq, a classified report landed on the desk of the chairman of the Joint Chiefs of Staff. It came from Defense Secretary Donald Rumsfeld, and it carried an ominous note.

“Please take a look at this material as to what we don’t know about WMD,” Rumsfeld wrote to Air Force General Richard Myers. “It is big.”

The report, revealed here publicly for the first time, was an inventory of what U.S. intelligence knew — or more importantly didn’t know — about Iraqi weapons of mass destruction. Its assessment was blunt: “We’ve struggled to estimate the unknowns.... We range from 0% to about 75% knowledge on various aspects of their program.”

Myers already knew about the report. The Joint Staff’s director for intelligence had prepared it, but Rumsfeld’s urgent tone said a great deal about how seriously the head of the Defense Department viewed the report’s potential to undermine the Bush administration’s case for war. But he never shared the eight-page report with key members of the administration such as then-Secretary of State Colin Powell or top officials at the CIA, according to multiple sources at the State Department, White House and CIA who agreed to speak on condition of anonymity. Instead, the report disappeared, and with it a potentially powerful counter-narrative to the administration’s argument that Saddam Hussein’s nuclear, chemical and biological weapons posed a grave threat to the U.S. and its allies, which was beginning to gain traction in major news outlets, led by the New York Times.

While the threat posed by a nuclear-armed Iraq was at the heart of the administration's case for war, the JCS report conceded: “Our knowledge of the Iraqi (nuclear) weapons program is based largely — perhaps 90 percent — on analysis of imprecise intelligence.”

No matter what aspect of Saddam’s WMD program was being discussed, the ambivalence in the report was the same.

The rationale for the invasion has long since been discredited, but the JCS report, now declassified, which a former Bush administration official forwarded in December, nevertheless has implications for both sides in the 2016 presidential race, in particular the GOP candidates who are relying for foreign policy advice on some of the architects of the war, and the Democratic front-runner, who once again is coming under fire from her primary opponent for supporting the invasion.

Then-Deputy Defense Secretary Paul Wolfowitz, whose military assistant was on the short list of people copied on the JCS report, is one of Jeb Bush’s foreign policy experts. Other supporters of the war, though they do not appear to have been aware of the JCS report, are involved in the various advisory roles in the 2016 campaign. John Bolton, former U.S. ambassador to the United Nations, is advising Ted Cruz; and Elliott Abrams and William Kristol are supporting Marco Rubio, whom Reuters reported is also briefed regularly by former Cheney adviser Eric Edelman.

The rise of ISIL and recent attacks in Paris and San Bernardino have given Democrat Bernie Sanders the ability to draw a straight line from the current Middle East chaos straight back to Clinton’s vote in favor of what he calls “one of the worst foreign policy blunders in the modern history of the United States,” a conflict that has claimed the lives of 4,500 Americans and some 165,000 Iraqis.

Rumsfeld was not under any legal or administrative obligation to circulate an internal DoD report, but not doing so raises questions about whether the administration withheld key information that could have undermined its case for war. Time and again, in the fall of 2002 and into early 2003, members of the administration spoke forcefully and without qualification about the threats they said Saddam Hussein posed. The JCS report undercut their assertions, and if it had been shared more widely within the administration, the debate would have been very different.

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The report originated with a question from the man whose obsession with “known unknowns” became a rhetorical trademark. On August 16, 2002, Rumsfeld asked Air Force Major General Glen Shaffer, head of the Joint Staff’s intelligence directorate, “what we don’t know (in a percentage) about the Iraqi WMD program,” according to a September 5 memo from Shaffer to Myers and three other senior military officials.

On September 5, Shaffer sent Myers his findings, titled “Iraq: Status of WMD Programs.” In a note to his boss, he revealed: “We don’t know with any precision how much we don’t know.”

And while the report said intelligence officials “assess Iraq is making significant progress in WMD programs,” it conceded that “large parts” of Iraq’s nuclear, chemical and biological weapons programs were concealed. As a result, “Our assessments rely heavily on analytic assumptions and judgment rather than hard evidence. The evidentiary base is particularly sparse for Iraqi nuclear programs.”

What Myers said when he received the report is not known, but by September 9, it had made its way across Rumsfeld’s desk, where it elicited his terse, typed summation: “This is big.”

But it wasn’t big enough to share with Powell, who in five months would be asked to make the U.S. case for war to the United Nations. Nor was it shared with other members of the National Security Council, according to former NSC staff. An intelligence official who was close to CIA Director George Tenet said he has no recollection of the report and said he would have remembered something that important.

U.S. Secretary of State Colin Powell (left) looks on as United Nations chief weapons inspector Hans Blix speaks on March 7, 2003. Mario Tama/Getty Images

Did President Bush see it? Or Vice President Dick Cheney? If they did, it didn’t temper what they said in public. Cheney had already kicked off the administration’s campaign in Nashville on August 27, saying, “the Iraqi regime has in fact been very busy enhancing its capabilities in the field of chemical and biological agents. And they continue to pursue the nuclear program they began so many years ago.”

This was the beginning of what White House chief of staff Andrew Card later called a campaign to “educate the public” about the threat from Iraq.

Rather than heed the JCS’ early warning — as well as similar doubts expressed by some CIA, State Department and Defense Intelligence Agency officers — and seek more reliable intelligence, Rumsfeld and Cheney turned to a parallel intelligence apparatus they created that relied largely on information from Iraqi defectors and a network of exiles led by the late Ahmed Chalabi and his Iraqi National Congress.

On Sunday, September 8, 2002 — three days after Shaffer reported that evidence on Iraq’s nuclear program was sparse — the Times’ Judith Miller and Michael Gordon led the newspaper with a report with the headline, “US Says Hussein Intensifies Quest for A-Bomb Parts.”

“Mr. Hussein’s dogged insistence on pursuing his nuclear ambitions, along with what defectors described in interviews as Iraq’s push to improve and expand Baghdad’s chemical and biological arsenals, have brought Iraq and the United States to the brink of war,” the Times wrote. The piece repeatedly cited anonymous senior Bush administration officials and Iraqi defectors.

Cheney, Rumsfeld, Powell and national security adviser Condoleezza Rice cited the Times story on talk shows that Sunday morning. Rice repeated a sentiment, credited in the Times story that "the first sign of a 'smoking gun' ... may be a mushroom cloud."

Chalabi later described himself and his supporters as “heroes in error.” One of the people relying on those errors was President Bush himself.

A month after Rumsfeld’s note to Myers, on October 7, Bush appeared at a VFW hall in Cincinnati, where he declared without reservation: Iraq “possesses and produces chemical and biological weapons. It is seeking nuclear weapons.”

Asked whether Rumsfeld had sent the cautionary intelligence report to the president, one senior member of the Joint Staff who was copied on it said he wasn’t certain, but added, “that’s the last place they would have sent it.”

The threat of Iraqi nuclear weapons was central to the administration’s effort to drum up public and political support for an invasion. “Mushroom clouds” were a leitmotif of speeches from Cheney and Rice. But the JCS report reveals the extent of the intelligence experts’ doubt and confusion on that subject:

“We think they possess a viable weapon design,” the report says, but qualified it repeatedly. “We do not know the status of enrichment capabilities”, it says, and: “We do not know with confidence the location of any nuclear-weapon-related facilities.”

No matter what aspect of Saddam’s WMD program was being discussed, the ambivalence in the report was the same. Was Iraq secretly reconstituting its biological weapons program, as Cheney had asserted in Nashville? The report’s answer: “We cannot confirm the identity of any Iraqi facilities that produce, test, fill, or store biological weapons.”

As for administration officials’ repeated claims that Iraq had mobile bioweapons plants, which in one especially colorful version were disguised as milk and yogurt trucks, the report says: “We believe Iraq has 7 mobile BW agent production plants but cannot locate them.” It summarizes the knowledge of Saddam’s germ warfare programs by saying: “Our knowledge of what biological weapons the Iraqis are able to produce is nearly complete our knowledge of how and where they are produced is nearly 90 percent incomplete.”

United States’ knowledge of Iraq’s chemical weapons, according to the JCS intelligence report was just as sketchy. “Our overall knowledge of the Iraqi CW program is primarily limited to infrastructure [and] doctrine. The specific agent and facility knowledge is 60-70 percent incomplete.”

But just because the JCS report wasn’t seen by key officials who might have benefited from its more cautious tone, doesn’t mean it wasn’t available for inspection.

“We do not know if all the processes required to produce a weapon are in place,” the report says, adding that the Iraqis “lack the precursors for sustained nerve agent production” and “we cannot confirm the identity of any Iraqi sites that produce final chemical agent.”

This did not prevent the president from telling his audience at the Cincinnati VFW hall in October, “We know that the regime has produced thousands of tons of chemical agents, including mustard gas, sarin nerve gas, VX nerve gas.” He added: “And surveillance photos reveal that the regime is rebuilding facilities that it had used to produce chemical and biological weapons.”

The JCS report, however, says U.S. intelligence was unable to "confirm the identity of any Iraqi sites that produce, test, fill or store biological weapons."

Finally, while advocates of an invasion also claimed that Iraq was developing longer range ballistic missiles capable of hitting Israel with weapons of mass destruction — Bush had made the claim before the U.N. General Assembly three days after Rumsfeld sent the report to Myers — the report says: “We doubt all processes are in place to produce longer range missiles.”

In February 2003, Powell appeared before the same body of foreign dignitaries to make the administration’s case, with CIA Director George Tenet sitting behind him:

“My colleagues, every statement I make today is backed up by sources, solid sources. These are not assertions. What we're giving you are facts and conclusions based on solid intelligence.”

Though it is easy to conclude the report was buried because it contained inconvenient truths, the precise reason it wasn’t circulated remains unclear. Efforts to reach Rumsfeld, directly and through an intermediary, were unsuccessful. Wolfowitz, his former deputy and a major advocate of toppling Saddam Hussein according to the 9/11 Commission report, did not return calls for comment. Myers, who knew as well as anyone the significance of the report, did not distribute it beyond his immediate military colleagues and civilian boss, which a former aide said was consistent with the role of the chairman of the Joint Chiefs. The report could have been divulged in a briefing by his staff to members of the Senate Armed Services Committee, but it wasn’t, probably because none of them was aware of its existence, according to former members of that committee.

Instead, on October 1, 2002, less than a month after the JCS report, the intelligence community produced a 92-page National Intelligence Estimate, or NIE, on Iraq’s WMD programs that made no mention of the report and instead claimed in its “Key Judgments” that: “We judge that Iraq has continued its weapons of mass destruction (WMD) programs in defiance of UN resolutions and restrictions. Baghdad has chemical and biological weapons as well as missiles with ranges in excess of UN restrictions; if left unchecked, it probably will have a nuclear weapon within this decade.”

Later, the NIE, an unclassified summary of which was made available to reporters two days after the Top Secret report was circulated, says: “We assess that Baghdad has begun renewed production of mustard, sarin GF (cyclosarin), and VX... ” It adds: “We judge that all key aspects — R&D, production, and weaponization — of Iraq’s offensive BW program are active and that most elements are larger and more advanced than they were before the Gulf war. Baghdad has mobile facilities for producing bacterial and toxin BW agents.” The NIE’s red flags and dissents, and it had a number, were subtle or tucked into footnotes.

Paul Pillar, at the time the national intelligence officer for the Near East who was involved in producing the NIE, said in a phone interview that he had never seen Shaffer's September 5 Pentagon report. When it was read to him, he called it an excellent summary of the limits of the U.S. intelligence community's knowledge about Saddam's WMD programs.

But just because the JCS report wasn’t seen by key officials who might have benefited from its more cautious tone, doesn’t mean it wasn’t available for inspection. Its middling “Secret” classification meant that, in theory, nothing would have prevented sharing the report's contents had any member of Congress requested a briefing from the Joint Chiefs of Staff.

For Clinton, then the junior senator from New York and a member of the Senate Foreign Relations Committee, the new evidence of early doubts raises a different question: How might her vote have changed if she and other lawmakers had known of the report's existence? Would she have taken it into account? The depth of her inquiry into the evidence has been called into question before. According to Her Way, a biography by New York Times reporters Jeff Gerth and Don Van Natta, Jr., Clinton never read the classified NIE. Clinton has never disputed that account, but she was not alone.

The Washington Post reported on April 27, 2004, after the invasion had begun going sour, that in the fall of 2002, before the vote on whether to invade Iraq, no more than six senators and few House members had logged into the Sensitive Compartmented Information Facility where they had to go to read the Top Secret estimate.